Could AI understand what the number one is and detect it in our real world same as AI can recognize cars and other things?
A understanding for this level of abstraction is technically possible.
It is not hard to create an AI able to count.
Unfortunately, this does not imply that the AI knows what 1 is.
It knows: This is 1 piece of cake and this is 1 sheet of paper.
But the idea of the number is not grasped yet. 
Also, animals can count, but they do not understand why it works. 

I would say that not even every human knows what 1 is:
The number, who is the neutral element of the multiplication.
The natural successor of 0. 

I can say with certainty, that there is no AI, who reached this level of abstraction.